Detecting apparatus



'June 30, 1959 G. B. LINDEVRMAN DETECTING APPARATUS Filed Ju1y'll, 1956 MODULATOR AMPLIFIER FIG.|

TUBE l l THYRATRON FIG. 4' 14 INVENTOR- GARRETT B. LINDERMAN ATTORNEY States Patent DETECTING APPARATUS B'. Linder'man, Washington, D.C., assignor to Linden-man Engineering Company, Inc., a corporation of Maryland Application July 11, 1956,'Serial'No. 597,268"

7 Claims. (Cl. 250-220) This invention relates to apparatus for detecting light transmission through material traversing] a predetermined path and is particularly intended for the detection of pin holes in sheet material, such as tin plate. One of the diificulties encountered with existing equipment involves the loss of the light, intended, to produce a response to the presence of a pin hole. employed in such apparatus, the occurrence. of a pin hole at: any substantial angle to the vertical will not be detected and the imperfect portion of the tin plate or-material: will not be marked or discarded.

Moreover, because of its lack' of sensitivity, most conventional apparatus has been limited in its operation to a'tin plate; speed of below approximately 50 feet per minute.

It, is: among the objects of this invention to overcome these difiiculties by using convergent reflectingmeans in conjunction with a light source and photosensitive means. Moreover, by using ultra violet light and appropriate filters to exclude light of other wave lengths, stray light from other sources will no longer present a problem.

In accordance with the present invention, the optical path preferably excludes lenses so that uncollimated light from the source will be transmitted through any pin holes which may exist, independent of their orientation, and then to the reflecting means and photosensitive means.

The apparatus of the present invention comprises a light source, photosensitive means responsive to light from the source, the source and responsive means being disposed on opposite sides of the path of the material under observation, amplifying means having an input circuit connected with the responsive means and an output circuit for energizing an actuator in response to light transmission through the material, and reflecting means convergent towards said photosensitive means interposed between said path and said photosensitive means. The reflecting means preferably comprises a plurality of plane surfaces. An optical filter is preferably interposed between the path of the material under observation and the reflecting means to exclude light of undesired wave lengths. The light source preferably produces ultra violet light which is readily passed by the optical filter and to which the light responsive means and associated amplifier will be sensitive. The actuator preferably includes a relay, which may be of the thyratron type, for actuating the usual marking device and/ or gate for separating imperfect material from that which is satisfactory. The photosensitive means preferably includes a plurality of interconnected photomultiplier tubes each provided with one of the converging reflecting means.

The pin hole detecting apparatus is combined with means for feeding the tin plate along its predetermined path so that the operation will be properly synchronized.

A more complete understanding of the invention will follow a description of the accompanying drawings wherein:

Fig. l is a somewhat diagrammatic showing of a circuit embodying the present invention;

When collimat'ed light is 2,892,95l Patented June 30, 1959.

Fig. 2 is a fragmentary plan view of a reflector assembly;

Fig. 3 is a section along line 3--3 of Fig. 2 with some of the reflectors removed;

Fig. 4 is a front elevation of a reflector; and

Fig. 5 is an end elevation of a reflector.

A supply circuit comprising an alternating current source 10 is connected by leads 12 and 14 with a modulator 16 wherein modulations at an elevated frequencyusually exceeding 2000 cycles per second, and prefer,- ably above 3000 cycles per second, are produced and delivered through leads 18 and 20 to a mercury lamp 22 serving as a source of ultra violet light. To facilitate starting, the lamp may contain neon in association with the mercury. Inasmuch as there are two light pulses for each cycle, if the frequency delivered by the modulator is 4000 cycles for example, the light pulses will be pro.- duced'at the rate of 8000 pulses per second. A reflector 24' is provided for the lamp'so as to redirect stray light downwardly towards the tin plate or other material 26 under observation. This material is fed in the usual manner as depicted for example in the disclosure of the patent to Rendel, 2,576,043, dated November 20, 1951. For simplicity of illustration, a feed roll 28 has been depicted in the attached, drawing as drivenby a motor 30 energized through leads 32, 34, 36 and 38' from the source 10, as in'copending application Serial No. 305,007, now Patent No. 2,758,712, filed August 18, 1952, of which this'is a continuation-impart.

Arranged. below the tin plate or other material under observation, an optical filter 40 is provided to exclude any light whose wave length varies appreciably from that of the source 22 operating at its predetermined modue lated"frequency. Below the'filter 40, photo-multiplier tubes 42 are arranged in a bank Within a housing 44 and connected in parallel by means of a cable 46 containing suitable conductors, to the input of an amplifier 50 which is sharply tuned to the rate of the light pulses produced by the source 22 and its modulator 16. The output of this amplifier is connected through leads carried by a cable 52 with a thyratron tube or relay 56 whose output is in turn connected through a lead 58 to the winding 60 of a relay 62 whose fixed and movable contacts 64 and 66 respectively, are connected with the source 10 through leads 32 and 38 in series with a winding 68 of a marking device 70. The thyratron 56, relay 62 and marking device 70 have been considered to constitute an actuator 72, which of course could eliminate some of these parts and substitute others. For example, as indicated in the Rendel patent to which reference has already been made, a gate or deflector might be employed with or in lieu of a marking device.

Moreover, timing mechanisms and other instrumentalities such as those depicted and described by Rendel are contemplated for association with the components illustrated here in diagrammatic form.

Interposed between the path of the material 26 undergoing observation and the photomultiplier tubes 42, refleeting means 48 are mounted providing reflecting surfaces converging towards the photomultiplier tubes so as to direct substantially all of the light passing through the material under observation to the photomultiplier tubes with a minimum of loss.

The individual reflectors 74, as shown in Figs. 2 to S inclusive, are of substantially I configuration in elevation as shown in Fig. 4 and have their surfaces directed towards the light source in divergent relationship as shown in Fig. 3, adjacent reflectors being disposed at an included angle of approximately 30.

The reflectors are mounted in a pair of notched strips 76, the upper notches 78 receiving the overhanging flanges 80 and the lower notches 82 receiving the lower overhanging flanges 84. Each reflector 74 constituting a pair converges towards its photomultiplier tube 42, as shown in Fig. 2, to provide a gap 86 through which collected and reflected light will be transmitted to such tube. Adjacent reflectors of successive pairs meet in substantially a linear edge 88 resulting from the beveled portions 90 formed on their upper flanges 80. Under these circumstances, there will be substantially no light reflected back towards the source from the reflectors, but instead, all of such light will be transmitted to the photo-multiplier tubes for which it is intended.

Whereas only one specific form of the invention has been illustrated in the drawings, those skilled in the art will recognize the many variations and applications which have already occurred to the present inventor. Accordingly, the scope of this invention should not be restricted to the illustrated example beyond the scope of the appended claims.

I claim:

1. Apparatus for detecting light transmission through material traversing a predetermined path comprising a light source, a row of photosensitive devices responsive to light from said source, said source and devices being disposed on opposite sides of said path, amplifying means having an input circuit connected with said devices and an output circuit for energizing an actuator in response to light transmission through said material, and reflecting means providing a pair of reflecting surfaces between each pair of said devices, the reflecting means being interposed between said path and said devices, and said surfaces of each pair diverging substantially from a line towards adjacent ones of said devices respectively.

2. Apparatus as set forth in claim 1 wherein said reflecting means comprises a plurality of substantially plane surfaces.

3. Apparatus as set forth in claim 1 wherein said photosensitive devices are interconnected photomultiplier tubes.

4. Apparatus as set forth in claim 1 wherein an optical filter is interposed between said path and said reflecting means.

5. Apparatus as set forth in claim 1 wherein said light source produces ultra violet light.

6. Apparatus as set forth in claim 1 wherein uncollimated light rays from said source are transmitted to said reflecting means.

7. Apparatus for detecting light transmission through material traversing a predetermined path comprising a light source, a row of photosensitive devices responsive to light from said source, said source and devices being disposed on opposite sides of said path, modulating means controlling said source to produce pulsations of light at a predetermined frequency, amplifying means sharply tuned to said frequency, said amplifying means having an input circuit connected with said devices and an output circuit for energizing an actuator in response to light transmission through said material, and reflecting means diverging substantially from a line interposed between said .path and said devices towards adjacent ones of said devices respectively.

References Cited in the file of this patent UNITED STATES PATENTS 1,976,120 Francis Oct. 9, 1934 2,027,595 Knobel et a1 Jan. 14, 1936 2,139,489 Cockrell Dec. 6, 1938 2,229,451 Gulliksen Jan. 21, 1941 2,312,626 Chamberlin et a1 Mar. 2, 1943 2,341,934 Martin Feb. 15, 1944 2,551,650 Urbach May 8, 1951 2,593,391 Bray Apr. 15, 1952 2,758,712 Linderman Aug. 14, 1956 2,762,930 Onksen et a1 Sept. 11, 1956 

